1. Field of the Invention
The present invention relates to a kneading disc segment and a twin-screw extruder having kneading screws each provided with the kneading disc segment.
2. Description of the Related Art
Generally, in a twin-screw extruder, polymeric resin pellets as matrix and a powdered additive are fed into a barrel and are fed to a downstream side while being kneaded by a pair of kneading screws inserted into the barrel, thereby a compound resin material such as a plastic compound is produced. The kneading screws are each provided with a central spline shaft and plural segments, the plural segments being fixed in a state in which the spline shaft extends therethrough, namely, fixed in a skewered state. Plural kinds of segments are known as segments constituting a kneading screw. In a kneading screw, these segments are combined axially to permit kneading suitable for predetermined use and material.
Among the segments referred to above, the segment particularly suitable for kneading is called a kneading segment. A rotor segment and a kneading disc segment are known as kneading segments. Particularly, a kneading disc segment is used in the case where a high degree of kneading is required.
A kneading disc segment is constituted by plate-like kneading discs each having a generally elliptical sectional shape perpendicular to the axial direction of a kneading screw, the kneading discs being arranged continuously side by side in the axial direction. In the kneading disc segment, the kneading discs rotate with rotation of the kneading screw, thereby the material to be kneaded is conducted to between the kneading discs and an inner wall of a barrel and is kneaded.
Two kinds of segments are known as kneading disc segments, which are classified according to the manner of mounting the kneading discs (mounting angle to a spline shaft). One is a feed kneading disc segment in which plural kneading discs are mounted continuously with a phase difference at a predetermined pitch of 30°-60° in a reverse rotational direction of a kneading screw. The other is a neutral kneading disc segment in which kneading discs are mounted continuously with a phase difference of 90° pitch.
The feed kneading disc segment has a feed capacity for the material to be kneaded because kneading discs are arranged twistedly in the axial direction. On the other hand, the neutral kneading disc segment has scarcely any feed capacity for the material. In the neutral kneading disc segment, therefore, kneading is easy to be done to a satisfactory extent because the material stays in the kneading section, and the degree of kneading can be enhanced in comparison with the feed kneading segment.
As the neutral kneading segment referred to above there is known, for example, such a neutral kneading segment as is disclosed in Japanese Patent Laid-Open Publication No. 2003-245534. This neutral kneading disc segment is disposed in an axially intermediate portion of a kneading screw and is composed of five kneading discs which are continuous in the axial direction. The five kneading discs are arranged in such a manner that adjacent discs intersect each other at an angle of 90° relative to the axis center of the kneading screw, thereby permitting a high kneading capacity to be exhibited.
The kinds of materials to be kneaded have recently been increasing and extruders are now required to exhibit a high kneading capacity than before.
The neutral kneading disc segment disclosed in the above Japanese patent laid-open publication No. 2003-245534 possesses a high kneading capacity as noted above, but even the degree of kneading attained by using the neutral kneading disc segment is not satisfactory in comparison with the degree of kneading required recently.